JP2023101533A - Zirconia sintered body, laminate and zirconia calcined body, and prosthesis for dentistry - Google Patents

Abstract

To provide a zirconia sintered body having elevated interlayer hardness of laminated powders.SOLUTION: The zirconia sintered body is obtained by laminating a plurality of zirconia powders containing zirconia and yttria as a stabilizer for suppression of phase transition of zirconia and having different compositions by different content ratio of pigments, oscillating to form mixed layers where zirconia powders in each boundary of zirconia powders in upper and lower layers are partially mixed with each other, and sintering the formed laminate, wherein specimens cut out from the zirconia sintered body with their longer direction being along with the lamination direction satisfy flexure hardness, a testing condition being in accordance with JISR1601, conducted to the specimens with the mixed layer existing in a manner to traverse the specimens along the load application direction, measured with load points of a three-point flexure test being aligned with positions of the mixed layer, of being 1100 MPa or over.SELECTED DRAWING: None

Description

[Description of related applications]
The present invention is based on Japanese Patent Application: Japanese Patent Application No. 2013-100617 (filed May 10, 2013), and the entire contents of the application are incorporated herein by reference.
The present invention relates to a zirconia sintered body. The present invention also relates to a laminate and a zirconia calcined body for producing a zirconia sintered body. Furthermore, the present invention relates to a dental prosthesis (prosthetic material) having a zirconia sintered body.

In dental treatment, artificial teeth are used as substitutes for natural teeth. This artificial tooth is required to have an appearance similar to that of a natural tooth.

US Pat. No. 5,300,000 discloses a multi-colored molded body having layers arranged on top of each other for producing a dental restoration. The molded body described in Patent Document 1 comprises (a) at least two consecutive different colored primary layers, and (b) at least two different colored intermediate layers between the at least two continuous different colored primary layers, wherein the change in color between the intermediate layers occurs in a direction opposite to the direction of the change in color between the primary layers.

JP-A-2008-68079

The entire disclosure of U.S. Pat. The following analysis is given in terms of the invention.

When producing a zirconia sintered body having a laminated structure as described in Patent Document 1, the zirconia powder of each layer is compression-molded such that the first layer is compression-molded and the second layer is compression-molded thereon. After stacking and sintering. However, even if the composition of each layer is the same except for a small amount of pigment, the zirconia powder may be delaminated at the boundary between adjacent layers during calcination or sintering. Also, in the sintered body, the strength of the boundary between adjacent layers is low, making it prone to partial destruction.

According to the first aspect of the present invention, there is provided a zirconia sintered body obtained by forming a mixed layer in which upper and lower zirconia powders are partially mixed at each boundary between zirconia powders, forming a mixed layer in which upper and lower zirconia powders are partially mixed at each boundary between the zirconia powders by laminating a plurality of zirconia powders having different compositions by laminating zirconia and yttria as a stabilizer that suppresses the phase transition of zirconia and yttria as a stabilizer that suppresses the phase transition of zirconia, and applying vibration to the zirconia sintered body. However, a zirconia sintered body is provided that satisfies the test condition that the bending strength measured by aligning the load point of the three-point bending test with the position of the mixed layer is 1100 MPa or more on the test piece in which the mixed layer exists so as to cross the test piece along the load application direction in accordance with JISR1601.

According to a second aspect of the present invention, there is provided a zirconia calcined body for producing a zirconia sintered body, which is sintered at 1400° C. to 1600° C. to obtain the zirconia sintered body according to the first aspect.

According to a third aspect of the present invention, there is provided a zirconia calcined body obtained by laminating a plurality of zirconia powders having different compositions by laminating zirconia and yttria as a stabilizer that suppresses the phase transition of zirconia and having different compositions due to different pigment contents, applying vibration to form a mixed layer in which upper and lower zirconia powders are partially mixed at each boundary between the zirconia powders, and calcining the laminated body at 800 ° C. to 1200 ° C., wherein the zirconia calcined body is obtained. Zirconia calcined satisfies the test condition that the bending strength measured by adjusting the load point of the three-point bending test to the position of the mixed layer is 90% or more of the bending strength of another test piece obtained by calcining one of the zirconia powders alone at the same temperature as the calcining temperature of the test piece. body is provided.

According to a fourth aspect of the present invention, there is provided a zirconia sintered body obtained by firing the zirconia calcined body according to the second aspect.

According to a fifth aspect of the present invention, there is provided a laminate for producing a zirconia sintered body, which is sintered at 1400° C. to 1600° C. to obtain the zirconia sintered body according to the first aspect.

According to a sixth aspect of the present invention, there is provided a laminate for producing a zirconia sintered body, which is fired at 800° C. to 1200° C. to obtain the zirconia calcined body according to the second aspect.

According to a seventh aspect of the present invention, there is provided a dental prosthesis in which the calcined zirconia body according to the second aspect is cut and then sintered.

According to the eighth perspective of the present invention, it is contained as a stabilizer as a stable agent that suppresses the transfer of zirconia and zirconia, and the pigment content is different and the composition is different, and the composition is different and vibration is given to vibrate the upper and lower zirconia powder at each boundary between the zirconia powder. It is a zirconia sintering body that forms a partially mixed layered layer and sintered at 1400 ° C. to 1600 ° C., which is a test piece that is cut out along the laminated direction from the zirconia sintering. For the above -mentioned test pieces that are crossing the test piece in line with the test piece, the bending strength measured by the priority of the three -point bending test according to the position of the mixed layer is that one of the zirconia powder is only 90 % of the bending strength of another test one of the exams at the same temperature as the sintered temperature of the test piece alone. A zirconia sintering is provided that meets the test conditions.

According to a ninth aspect of the present invention, a zirconia calcined body obtained by laminating zirconia and yttria as a stabilizer that suppresses the phase transition of zirconia and having different compositions by laminating a plurality of zirconia powders having different compositions due to different pigment contents to form a mixed layer in which upper and lower zirconia powders are partially mixed at each boundary between the zirconia powders, forming a mixed layer, and calcining the laminated body at 800 ° C. to 1200 ° C., said zirconia calcined body. Zirconia calcined satisfies the test condition that the bending strength measured by adjusting the load point of the three-point bending test to the position of the mixed layer is 90% or more of the bending strength of another test piece obtained by calcining one of the zirconia powders alone at the same temperature as the calcining temperature of the test piece. body is provided.

The present invention has at least one of the following effects.

According to the zirconia sintered body of the present invention, even when a zirconia sintered body is produced by laminating zirconia powders having different compositions, it is possible to obtain a zirconia sintered body in which the strength of the boundary between layers is not particularly reduced.

According to the laminated body and the zirconia calcined body of the present invention, the zirconia sintered body as described above can be obtained.

The schematic diagram for demonstrating a three-point bending test method. Schematic diagram of a zirconia sintered body. The schematic diagram of the test piece for measuring the deformation amount at the time of sintering. The schematic diagram of the test piece for measuring the deformation amount at the time of sintering. The schematic diagram for demonstrating the measuring method of deformation. Schematic diagram and measurement results of a test piece in Example 5. FIG. Schematic diagram and measurement results of a test piece in Comparative Example 3. FIG.

Preferred forms of each of the above viewpoints are described below.

According to a preferred embodiment of the first aspect, the bending strength is 1200 MPa or more.

According to the preferred embodiment of the first aspect, when a zirconia calcined body is produced by calcining a laminate at 800 ° C. to 1200 ° C., the bending strength measured by aligning the load point of a three-point bending test with the position of the boundary in a 3-point bending test for a test piece of the calcined body in which the boundary of a plurality of zirconia powders exists so as to cross the test piece in accordance with JISR 1601 is calcined at the same temperature as the calcination temperature of the test piece. It is 90% or more of the bending strength of the calcined zirconia calcined body.

According to the preferred embodiment of the first aspect, the plurality of zirconia powders contain pigments and have different pigment contents.

According to the preferred embodiment of the first aspect, each sintered body obtained by sintering a plurality of zirconia powders alone at 1500° C. has a bending strength of 1100 MPa or more as measured according to JISR1601.

According to the preferred embodiment of the first aspect, a zirconia calcined body is produced by calcining the laminate at 800 ° C. to 1200 ° C., and the zirconia calcined body is molded into a rectangular parallelepiped shape with dimensions of 50 mm in width × 10 mm in height × 5 mm in depth as a test piece. When baked at 0° C. for 2 hours and placed with the bottom surface deformed into a concave surface facing down among the two bottom surfaces, (maximum distance between the bottom surface deformed into a concave surface and the contact surface)/(distance between the contact portions in the width direction)×100 is 0.15 or less.

According to the preferred form of the first viewpoint, L^*a^*b^*Chromaticity (L^*, a^*, b^*) is (L1, a1, b1), and the second point L in the section from the other end to 25% of the total length^*a^*b^*Chromaticity (L^*, a^*, b^*) is (L2, a2, b2), L1 is 58.0 or more and 76.0 or less, a1 is -1.6 or more and 7.6 or less, b1 is 5.5 or more and 26.7 or less, L2 is 71.8 or more and 84.2 or less, a2 is -2.1 or more and 1.8 or less, b2 is 1.9 or more and 16.0 or less, L1 < L2, and a1 > a2 Yes, b1>b2, and from the first point to the second point L^*a^*b^*There is no change in the tendency of chromaticity to increase or decrease depending on the color system.

According to the preferred form of the first viewpoint, on the straight line connecting the first point and the second point, there is no section in which the L ^{* value decreases by 1 or more from the first point to the second point, there is no section in which the a* value} increases by 1 or more from the first point to the second point, and there is no section in which the b ^* value increases by 1 or more from the first point to the second point.

According to the preferred embodiment of the first viewpoint, when the chromaticity (L ^* , a ^* , b ^* ) according to the L ^* a ^* b ^* color system at the third point between the first point and the second point on the straight line connecting the first point and the second point is (L3, a3, b3), L3 is 62.5 or more and 80.5 or less, a3 is -1.8 or more and 5.5 or less, and b3 is 4.8 or more and 21.8 or less. , L1<L3<L2, a1>a3>a2, and b1>b3>b2.

According to the preferred form of the first viewpoint, when the chromaticity (L ^* , a ^* , b ^* ) according to the L ^* a ^* b ^* color system at the fourth point between the third point and the second point on the straight line connecting the first point and the second point is (L4, a4, b4), L4 is 69.1 or more and 82.3 or less, a4 is −2.1 or more and 1.8 or less, and b4 is 3.5 or more and 16.2 or less. , a1>a3>a4>a2 and b1>b3>b4>b2.

According to a preferred form of the first viewpoint, the third point is at a distance of 45% of the total length from one end. The fourth point is 55% of the total length from one end.

According to the preferred form ^of the first viewpoint, at the first point, the third point, the fourth point, and the second point, ΔL ^* is the difference in the L ^* value at the two adjacent points, Δa ^* is the difference in the a ^* value at the two adjacent points, and Δb ^* is the difference in the b ^* value at the two adjacent points. ΔE ^* ab between the fourth points is 1.8 or more and 17.9 or less, and ΔE ^* ab between the fourth points ^and the second points is 1.0 or more and 9.0 or less.

Formula 1

According to the preferred form of the first viewpoint, when the chromaticity (L ^* , a ^* , b ^* ) according to the L ^* a ^* b ^* color system at the third point between the first point and the second point on the straight line connecting the first point and the second point is (L3, a3, b3), L3 is 69.1 or more and 82.3 or less, a3 is -2.1 or more and 1.8 or less, and b3 is 3.5 or more and 16.2 or less. , L1<L3<L2, a1>a3>a2, and b1>b3>b2.

According to the preferred form of the first viewpoint, the color changes in the first direction from one end to the other end, and the tendency of increase or decrease in chromaticity according to the L ^* a ^* b ^* color system does not change on the straight line from one end to the other end.

According to the preferred form of the first aspect, the L ^* value tends to increase from the first point to the second point on the straight line connecting one end and the other end, and the a ^* value and b ^* value tend to decrease.

According to a preferred form of the first aspect, the distance from one end to the other end is 5 mm to 18 mm.

According to the preferred form of the first viewpoint, the color does not change along the second direction orthogonal to the first direction.

According to the preferred form of the first viewpoint, ΔL ^* is the difference in L ^* value between the two points, Δa ^* is the difference in a ^* value between the two points, Δb ^* is the difference in b ^* value between the two points, and ΔE ^* ab is calculated from Equation 1 above, and ΔE ^* ab is less than 1 at two points on a straight line extending in the second direction.

According to a preferred embodiment of the first aspect, the fracture toughness measured according to JISR1607 is 3.5 MPa·m ^1/2 or more.

According to the preferred embodiment of the first aspect, in the X-ray diffraction pattern of the zirconia sintered body after being subjected to a hydrothermal treatment test at 180 ° C. and 1 MPa for 5 hours, the tetragonal crystal-derived [111] peak at 2θ near 30 ° occurs.

According to the preferred embodiment of the third aspect, the plurality of zirconia powders contain pigments and have different pigment content rates.

According to the preferred embodiment of the third aspect, a zirconia calcined body is produced by calcining the laminate at 800 ° C. to 1200 ° C., and the zirconia calcined body is molded into a rectangular parallelepiped shape with dimensions of 50 mm in width × 10 mm in height × 5 mm in depth as a test piece. When baked at 0° C. for 2 hours and placed with the bottom surface deformed into a concave surface facing down among the two bottom surfaces, (maximum distance between the bottom surface deformed into a concave surface and the contact surface)/(distance between the contact portions in the width direction)×100 is 0.15 or less.

According to the preferred embodiment of the seventh aspect, cutting is performed using a CAD/CAM system.

In the present invention, for example, when the zirconia sintered body has a crown shape, the above-mentioned "one end" and "the other end" preferably refer to one point on the incisal side and one point on the root side. The one point may be one point on the end face or one point on the cross section. A point located within 25% of the total length from one end or the other end means, for example, a point at a distance corresponding to 10% of the height of the crown from the one end or the other end.

When the zirconia sintered body has a disk shape or a hexahedral shape such as a rectangular parallelepiped, the above-mentioned "one end" and "the other end" preferably refer to one point on the upper surface and the lower surface (bottom surface). The one point may be one point on the end face or one point on the cross section. A point in a section from one end or the other end to 25% of the total length means, for example, a point at a distance corresponding to 10% of the thickness of the hexahedron or disc from the one end or the other end.

In the present invention, "the first direction from one end to the other end" means the direction in which the color changes. For example, the first direction is preferably the direction in which the powder is layered in the manufacturing method described below. For example, when the zirconia sintered body has a crown shape, the first direction is preferably the direction connecting the incisal side and the root side.

A zirconia sintered body of the present invention will be described. The zirconia sintered body of the present invention is a sintered body in which partially stabilized zirconia crystal grains are mainly sintered, and has partially stabilized zirconia as a matrix phase. In the zirconia sintered body of the present invention, the main crystal phase of zirconia is a tetragonal system or a tetragonal system and a cubic system. It is preferable that the zirconia sintered body does not substantially contain a monoclinic system (at the stage before the hydrothermal treatment test described later).

The zirconia sintered body of the present invention includes not only a sintered body obtained by sintering molded zirconia particles under normal pressure or no pressure, but also a sintered body densified by high temperature pressure treatment such as HIP (Hot Isostatic Pressing) treatment.

The zirconia sintered body of the present invention contains zirconia and its stabilizer. The stabilizer suppresses phase transition of tetragonal system zirconia to monoclinic system. By suppressing the phase transition, strength, durability and dimensional accuracy can be enhanced. Examples of stabilizers include oxides such as calcium oxide (CaO), magnesium oxide (MgO), yttrium oxide (Y ₂ O ₃ ) (hereinafter referred to as “yttria”), and cerium oxide (CeO ₂ ). The stabilizer is preferably added in such an amount that the tetragonal zirconia particles can be partially stabilized. For example, when yttria is used as a stabilizer, the content of yttria is preferably 2.5 mol % to 5 mol %, more preferably 3 mol % to 4.5 mol %, and more preferably 3.5 mol % to 4.5 mol %, relative to the total number of moles of zirconia and yttria. If the content of the stabilizer is too high, the bending strength and fracture toughness will decrease even if the phase transition can be suppressed. On the other hand, if the content of the stabilizer is too low, the progress of phase transition cannot be sufficiently suppressed, even if the decrease in bending strength and fracture toughness can be suppressed. Tetragonal zirconia partially stabilized by adding a stabilizer is called partially stabilized zirconia (PSZ).

The zirconia sintered body of the present invention preferably contains aluminum oxide (Al ₂ O ₃ ; alumina). Preferably, the aluminum oxide is alpha alumina. The strength can be increased by containing aluminum oxide. The content of aluminum oxide in the zirconia sintered body is preferably 0% by mass (not included) to 0.3% by mass with respect to the total mass of zirconia and stabilizer. If the content of aluminum oxide exceeds 0.3% by mass, the transparency is lowered.

The zirconia sintered body of the present invention preferably contains titanium oxide (TiO ₂ ; titania). Grain growth can be promoted by containing titanium oxide. The content of titanium oxide in the zirconia sintered body is preferably 0% by mass (not included) to 0.6% by mass with respect to the total mass of zirconia and stabilizer. If the content of titanium oxide exceeds 0.6% by mass, the strength will decrease.

In the zirconia sintered body of the present invention, the content of silicon oxide (SiO ₂ ; silica) is preferably 0.1% by mass or less with respect to the total mass of zirconia and the stabilizer, and the zirconia sintered body preferably contains substantially no silicon oxide. This is because the presence of silicon oxide lowers the transparency of the zirconia sintered body. Here, the term "substantially does not contain" means that the properties and characteristics of the present invention are not particularly affected, and preferably does not exceed the impurity level, and does not necessarily mean that it is less than the detection limit.

The zirconia sintered body of the present invention may contain a coloring pigment. When the zirconia sintered body is applied to dental materials, pigments such as chromium oxide (Cr ₂ O ₃ ), erbium oxide (Er ₂ O ₃ ), iron oxide (Fe ₂ O ₃ ), praseodymium oxide (Pr ₆ O ₁₁ ), etc. can be used. These pigments may be used in combination. The pigment content can vary locally.

For example, when a zirconia sintered body used as a dental material contains chromium oxide, the partial content of chromium oxide in the region containing chromium oxide is preferably 0.001% by mass or less with respect to the total mass of zirconia and the stabilizer. When the zirconia sintered body used as a dental material contains erbium oxide, the partial content of erbium oxide in the region containing erbium oxide is preferably 2% by mass or less with respect to the total mass of zirconia and the stabilizer. For example, when a zirconia sintered body used as a dental material contains iron oxide, the partial content of iron oxide in the region containing iron oxide is preferably 0.1% by mass or less with respect to the total mass of zirconia and the stabilizer. For example, when a zirconia sintered body used as a dental material contains praseodymium oxide, the partial content of praseodymium oxide in the region containing praseodymium oxide is preferably 0.1% by mass or less with respect to the total mass of zirconia and the stabilizer.

After sintering the zirconia sintered body, a hydrothermal treatment test (described later), which is an accelerated deterioration test. In the X-ray diffraction pattern of the untreated zirconia sintered body measured with CuKα rays, the peak (hereinafter referred to as the "first peak") present near the position where the [111] peak derived from the tetragonal crystal near 2θ near 28 ° occurs. The height ratio (that is, “second peak height/first peak height”; hereinafter referred to as “monoclinic peak ratio”) is preferably 0.1 or less, more preferably 0.05 or less.

In the zirconia sintered body of the present invention, progress of phase transition from tetragonal to monoclinic is suppressed even after a hydrothermal treatment test. For example, when the zirconia sintered body of the present invention is subjected to hydrothermal treatment at 180 ° C. and 1 MPa for 5 hours, the X-ray diffraction pattern measured with CuKα rays on the surface of the zirconia sintered body after the hydrothermal treatment shows a monoclinic peak ratio of preferably 1 or less, more preferably 0.8 or less, further preferably 0.7 or less, and further preferably 0.6 or less.

In this document, the term "hydrothermal treatment test" refers to a test conforming to ISO13356. However, the conditions specified in ISO 13356 are "134°C, 0.2 MPa, 5 hours", but in the present invention, in order to make the test conditions more severe, the conditions are set to "180°C, 1 MPa", and the test time is set as appropriate according to the purpose. The hydrothermal treatment test is also called "low temperature accelerated deterioration test" or "hydrothermal deterioration test".

The zirconia sintered body of the present invention preferably has a bending strength of 1000 MPa or more, more preferably 1100 MPa or more, and even more preferably 1200 MPa or more, as measured according to JISR1601. Note that these are numerical values in the state of not being subjected to the hydrothermal treatment test.

In the zirconia sintered body of the present invention, the bending strength described above can be obtained in a three-point bending test even when the load point is positioned at the boundary between layers in the manufacturing method described below. FIG. 1 shows a schematic diagram of the three-point bending test. For example, in the test piece, the boundary between zirconia powders having different compositions is positioned at the center of the test piece (middle in the longitudinal direction). The boundary extends along the direction of load application (along the direction of the smallest area) and traverses the test piece. The load points for the 3-point bending test are aligned with the locations of the boundaries. Even if the flexural strength is measured by such a test in which a load is applied to the boundary, a strength similar to that of a sintered body that is not laminated (no boundary) can be obtained. For example, in the sintered body of the present invention, the bending strength measured by applying a load to the boundary between layers is preferably 90% or more, more preferably 95% or more, of the bending strength of a region other than the boundary (for example, the bending strength of a calcined body produced from a non-laminated composition under the same conditions (for example, the same calcination temperature and calcination time)).

The zirconia sintered body of the present invention preferably has a fracture toughness measured in accordance with JISR1607 of 3.5 MPa m ^1/2 or more, more preferably 3.8 MPa m ^1/2 or more, even more preferably 4 MPa m ^1/2 or more, and more preferably 4.2 MPa m ^1/2 or more. Note that these are numerical values in an untreated state of the hydrothermal treatment test.

In the zirconia sintered body of the present invention, the above fracture toughness can be obtained in a fracture toughness measurement test even when the load point is positioned at the boundary between layers in the manufacturing method described below. For example, in the test piece, the boundary between zirconia powders having different compositions is positioned at the center of the test piece (middle in the longitudinal direction). The boundary extends along the direction of load application (along the direction of the smallest area) and traverses the test piece. The position of the diamond indenter for the measurement test is aligned on the boundary. Even if the fracture toughness is measured by a test in which a load is applied to the boundary in this way, it is possible to obtain the same fracture toughness as that of a sintered body that is not laminated (no boundary).

The zirconia sintered body of the present invention preferably satisfies the above numerical values for all of the monoclinic peak ratio, bending strength and fracture toughness after hydrothermal treatment. For example, the zirconia sintered body of the present invention preferably has a monoclinic peak ratio of 1 or less after hydrothermal treatment, a fracture toughness of 3.5 MPa·m ^1/2 or more, and a bending strength of 1000 MPa or more. More preferably, the zirconia sintered body of the present invention has a monoclinic peak ratio of 0.6 or less after hydrothermal treatment, a fracture toughness of 4 MPa·m ^1/2 or more, and a bending strength of 1000 MPa or more.

When the zirconia sintered body of the present invention is colored, especially when the color gradually changes (gradation) in one direction, the zirconia sintered body of the present invention preferably has a direction in which the color does not substantially change. FIG. 2 shows a schematic diagram of a zirconia sintered body. For example, in the zirconia sintered body 10 shown in FIG. 2, it is preferable that the color in the first direction X does not substantially change. For example, between any two points on a straight line extending in the first direction X, the difference between ^the L ^* value, a ^* value, and b ^* value, which are chromaticities in the L ^* a ^* b ^* color system (JISZ8729), is ΔL ^* , Δa ^* , and ^{Δb *} , respectively.

formula 2

Moreover, when the zirconia sintered body of the present invention is colored, it is preferable that the color changes (has a gradation) from one end connecting both ends to the other end. On the straight ^line extending in the second direction Y from one end P to the other end Q of the zirconia sintered body 10 ^shown in ^FIG . That is, when the L ^* value tends to increase on a straight line from one end P to the other end Q, it is preferable that there is no section where the L ^* value substantially decreases. For example, when the L ^* value tends to increase on a straight line from one end P to the other end Q, it is preferable that there is no section where the L ^* value decreases by 1 or more, and more preferably there is no section where the L* value decreases by 0.5 or more. When the a ^* value tends to decrease on the straight line from the one end P to the other end Q, it is preferable that there is no section where the a ^* value substantially increases. For example, when the a ^* value tends to decrease on a straight line from one end P to the other end Q, it is preferable that there is no section where the a ^* value increases by 1 or more, and more preferably there is no section where the a* value increases by 0.5 or more. Further, when the b ^* value tends to decrease on the straight line from the one end P to the other end Q, it is preferable that there is no section where the b ^* value substantially increases. For example, when the b ^* value tends to decrease on a straight line from one end P to the other end Q, it is preferable that there is no interval in which the b ^* value increases by 1 or more, and more preferably there is no interval in which the b* value increases by 0.5 or more.

As for the direction of color change in the zirconia sintered body 10, it is preferable that the a ^* value and the b ^* value tend to decrease from one end P to the other end Q when the L ^* value tends to increase. For example, when the zirconia sintered body 10 is used as a dental prosthetic material, it is preferable that the color changes from light yellow, light orange, or light brown to white from one end P to the other end Q.

In FIG. 2, points on a straight line connecting one end P to the other end Q are defined as a first point A, a second point B, a third point C, and a fourth point D in order from the one end P side. When the zirconia sintered body 10 is used as a dental prosthetic material, the first point A is from one end P to 25% to 45% of the length between one end P and the other end Q (hereinafter referred to as "total length"). It is preferable that the second point B is in a section from a point 30% of the total length from the one end P to 70% of the total length from the one end P. It is preferable that the fourth point D is located in a section from the other end Q to 25% to 45% of the total length. It is preferable that the third point C is located in a section from a point 30% of the total length away from the other end Q to 70% of the total length from the other end Q.

Let the chromaticities (L ^* , a ^* , b ^* ) of the zirconia sintered body 10 according to the L ^* a ^* b ^* color system (JISZ8729) at the first point A, the second point B, the third point C, and the fourth point D be (L1, a1, b1), (L2, a2, b2), (L3, a3, b3), and (L4, a4, b4). At this time, it is preferable that the following magnitude relationship is established. The chromaticity of each point can be obtained by producing a zirconia sintered body of a single composition corresponding to each point and measuring the chromaticity of the zirconia sintered body.

L1<L2<L3<L4
a1>a2>a3>a4
b1>b2>b3>b4

When applying the zirconia sintered body of the present invention to a dental material, for example, L1 is preferably 58.0 or more and 76.0 or less. L2 is preferably 62.5 or more and 80.5 or less. L3 is preferably 69.1 or more and 82.3 or less. L4 is preferably 71.8 or more and 84.2 or less.

When the zirconia sintered body of the present invention is applied to dental materials, for example, a1 is preferably -1.6 or more and 7.6 or less. a2 is preferably -1.8 or more and 5.5 or less. a3 is preferably -2.1 or more and 1.6 or less. a4 is preferably -2.1 or more and 1.8 or less.

When applying the zirconia sintered body of the present invention to a dental material, for example, b1 is preferably 5.5 or more and 26.7 or less. b2 is preferably 4.8 or more and 21.8 or less. b3 is preferably 3.5 or more and 16.2 or less. b4 is preferably 1.9 or more and 16.0 or less.

When the zirconia sintered body of the present invention is applied to a dental material, preferably L1 is 60.9 or more and 72.5 or less, a1 is 0.2 or more and 5.9 or less, b1 is 11.5 or more and 24.9 or less, L4 is 72.2 or more and 79.2 or less, a4 is −1.2 or more and 1.7 or less, and b4 is 6.0 or more and 15.8 or less. More preferably, L1 is 63.8 or more and 68.9 or less, a1 is 2.0 or more and 4.1 or less, b1 is 17.5 or more and 23.4 or less, L4 is 72.5 or more and 74.1 or less, a4 is −0.2 or more and 1.6 or less, and b4 is 10.1 or more and 15.6 or less. This allows matching to average tooth shades.

The color difference ΔE ^* ab between two adjacent points can be expressed by the following formula. ΔL ^* is the difference in L ^* values (eg, L1−L2) in two adjacent layers. Δa ^* is the difference in a ^* values (eg, a1−a2) in two adjacent layers. Δb ^* is the difference in b ^* values (eg, b1-b2) in two adjacent layers. When the color difference between the first point A and the second point B is ΔE ^* ab1, the color difference between the second point B and ^the third point C is ΔE ^* ab2, and the color difference between the third point C and the fourth point D is ΔE ^* ab3. ΔE ^* ab2 is preferably 1.8 or more and 17.9 or less. ΔE ^* ab3 is preferably 1.0 or more and 9.0 or less. This makes it possible to reproduce color change similar to that of natural teeth.

Formula 3

When the color difference between the first point A and the fourth point D is ΔE ^* ab4, and the chromaticities of the first point A, the second point B, the third point C, and the fourth point D have the above relationship, for example, ΔE ^* ab4 is preferably 36 or less. The sum of the color difference ΔE ^* ab1 between the first point A and the second point B, the color difference ΔE ^* ab2 between the second point B and the third point C, and the color difference ΔE*ab3 between the third point C and the fourth point minus the color difference ^{ΔE *} ab4 between the first point A and the fourth point D is preferably 1 or less. This makes it possible to show natural color changes.

In the zirconia sintered body of the present invention, when powders of different compositions are laminated in the manufacturing method described later, the continuous change in the b ^* value of the L ^* a ^* b ^* color system ⁽ JISZ8729) is measured on a straight line that traverses the layers (crossing the boundaries), that is, along the second direction Y shown in FIG. Moreover, even when crossing the boundary portion, it is preferable that no sudden increase or decrease in the b ^* value is observed. The change in the b ^* value can be measured using, for example, a two-dimensional colorimeter RC-300 manufactured by PaPaLab Co., Ltd. In this measurement, the spacing between adjacent measurement points can be set to 13 μm, for example.

When the zirconia sintered body of the present invention is applied to a dental material, if the chromaticity of the fourth point D is within the above range, a zirconia sintered body is produced solely from the composition corresponding to the fourth point, and both sides are mirror-finished to prepare a sample with a thickness of 0.5 mm, and the light transmittance measured according to JISK7361 is preferably 27% or more. Further, when the chromaticity of the first point A is within the above range, a zirconia sintered body is produced solely from the composition corresponding to the first point, and a sample with a thickness of 0.5 mm is produced by mirror-finishing both surfaces.

When the zirconia sintered body of the present invention is applied to a dental material, the length L in the first direction Y of the zirconia sintered body 10 of the present invention preferably satisfies at least the length corresponding to the exposed portion of the natural tooth. For example, the length L of the zirconia sintered body 10 is preferably 5 mm to 18 mm.

Next, the composition and calcined body for producing the zirconia sintered body of the present invention will be described. The composition and the calcined body are to be the precursor (intermediate product) of the above-described zirconia sintered body of the present invention. The calcined body is obtained by sintering (that is, calcining) the composition at a temperature that does not lead to sintering. The calcined body also includes a molded body. For example, the calcined body also includes a dental prosthesis (for example, a crown shape) obtained by processing a calcined zirconia disk with a CAD/CAM (Computer-Aided Design/Computer-Aided Manufacturing) system.

The composition and the calcined body of the present invention are produced by laminating zirconia powders having different compositions.

The composition and calcined body contain (predominantly monoclinic) zirconia crystal grains, a stabilizer, and titanium oxide. The composition may contain aluminum oxide. Preferably, the aluminum oxide is alpha alumina.

The average particle size of the zirconia powder (granular state) in the composition is preferably 20 μm to 40 μm.

Examples of stabilizers in the composition and calcined body include oxides such as calcium oxide (CaO), magnesium oxide (MgO), yttria, and cerium oxide (CeO ₂ ). The stabilizer is preferably added in such an amount that the zirconia particles in the sintered body can be partially stabilized. For example, when yttria is used as a stabilizer, the content of yttria is preferably 2.5 mol % to 4.5 mol %, preferably 3 mol % to 4.5 mol %, more preferably 3.5 mol % to 4.5 mol %, relative to the total number of moles of zirconia and yttria.

The content of aluminum oxide in the composition and the calcined body is preferably 0% by mass (not included) to 0.3% by mass with respect to the total mass of the zirconia crystal grains and the stabilizer. This is for increasing the strength of the zirconia sintered body. If it is more than 0.3% by mass, the transparency of the zirconia sintered body is lowered.

The content of titanium oxide in the composition and the calcined body is preferably 0% by mass (not included) to 0.6% by mass with respect to the total mass of the zirconia crystal grains and the stabilizer. This is for grain growth of zirconia crystals. If it is more than 0.6% by mass, the strength of the zirconia sintered body will decrease.

In the composition and the calcined body of the present invention, the content of silicon oxide is preferably 0.1% by mass or less with respect to the total mass of the zirconia crystal grains and the stabilizer, and the composition and the calcined body preferably do not substantially contain silicon oxide (SiO ₂ ; silica). This is because the presence of silicon oxide lowers the transparency of the zirconia sintered body. Here, the term "substantially does not contain" means that the properties and characteristics of the present invention are not particularly affected, and preferably does not exceed the impurity level, and does not necessarily mean that it is less than the detection limit.

The composition and calcined body of the present invention may contain pigments for coloring. For example, when a zirconia sintered body produced from the composition and calcined body of the present invention is applied to a dental material, pigments such as chromium oxide (Cr ₂ O ₃ ), erbium oxide (Er ₂ O ₃ ), iron oxide (Fe ₂ O ₃ ), praseodymium oxide (Pr ₆ O ₁₁ ), and the like can be used. These pigments may be used in combination. The pigment content can also be partially different.

For example, in the molded composition and calcined body, the whole is divided into four layers, the first layer is a region of 25% to 45% of the total thickness from the bottom end, the second layer is a region of 5% to 25% of the total thickness on the first layer, the third layer is a region of 5% to 25% of the total thickness on the second layer, and the fourth layer is a region of 25% to 45% of the total thickness from the top of the third layer to the top. It is preferred that the pigment content decreases from the fourth layer to the fourth layer.

For example, when using the sintered body produced from the composition and the calcined body as a dental material, erbium oxide and iron oxide can be added as pigments. In this case, the first layer preferably has an erbium oxide content of 0.33% by mass to 0.52% by mass and an iron oxide content of 0.05% by mass to 0.12% by mass, based on the total mass of zirconia and stabilizer. In the second layer, the content of erbium oxide is preferably 0.26% by mass to 0.45% by mass, and the content of iron oxide is preferably 0.04% by mass to 0.11% by mass, based on the total mass of zirconia and stabilizer. In the third layer, the content of erbium oxide is preferably 0.05% to 0.24% by mass, and the content of iron oxide is preferably 0.012% to 0.08% by mass, based on the total mass of zirconia and stabilizer. In the fourth layer, the content of erbium oxide is preferably 0% to 0.17% by mass, and the content of iron oxide is preferably 0% to 0.07% by mass, based on the total mass of zirconia and stabilizer. It is preferable that the contents of erbium oxide and iron oxide decrease in order from the first layer to the fourth layer.

For example, when the sintered body produced from the composition and the calcined body is used as a dental material, erbium oxide, iron oxide and chromium oxide can be added as pigments. For example, when a sintered body produced from the composition and the calcined body is used as a dental material, the first layer preferably has an erbium oxide content of 0.08% by mass to 0.37% by mass, an iron oxide content of 0.08% by mass to 0.15% by mass, and a chromium oxide content of 0.0008% by mass to 0.0012% by mass, based on the total mass of the zirconia and the stabilizer. In the second layer, the content of erbium oxide is preferably 0.06% to 0.42% by mass, the content of iron oxide is 0.06% to 0.18% by mass, and the content of chromium oxide is preferably 0.0006% to 0.001% by mass, based on the total mass of zirconia and the stabilizer. In the third layer, the content of erbium oxide is preferably 0.06% to 0.17% by mass, the content of iron oxide is 0.018% to 0.042% by mass, and the content of chromium oxide is preferably 0.0001% to 0.0003% by mass, based on the total mass of zirconia and the stabilizer. In the fourth layer, the content of erbium oxide is preferably 0% by mass to 0.12% by mass, the content of iron oxide is 0% by mass to 0.001% by mass, and the content of chromium oxide is preferably 0% by mass to 0.0001% by mass, based on the total mass of zirconia and the stabilizer. It is preferable that the contents of erbium oxide, iron oxide and chromium oxide decrease in order from the first layer to the fourth layer.

For example, when the sintered body produced from the composition and the calcined body is used as a dental material, erbium oxide, iron oxide and praseodymium oxide can be added as pigments. For example, when a sintered body produced from the composition and the calcined body is used as a dental material, the first layer preferably has an erbium oxide content of 0.08% by mass to 2.2% by mass, an iron oxide content of 0.003% by mass to 0.12% by mass, and a praseodymium oxide content of 0.003% by mass to 0.12% by mass, based on the total mass of zirconia and stabilizer. In the second layer, the content of erbium oxide is preferably 0.06% to 1.9% by mass, the content of iron oxide is 0.002% to 0.11% by mass, and the content of praseodymium oxide is preferably 0.002% to 0.11% by mass, based on the total mass of zirconia and stabilizer. In the third layer, the erbium oxide content is preferably 0.018% by mass to 1% by mass, the iron oxide content is preferably 0.008% by mass to 0.06% by mass, and the praseodymium oxide content is preferably 0.0008% by mass to 0.06% by mass, based on the total mass of zirconia and the stabilizer. In the fourth layer, it is preferable that the content of erbium oxide is 0% to 0.7% by mass, the content of iron oxide is 0% to 0.05% by mass, and the content of praseodymium oxide is 0% to 0.05% by mass, based on the total mass of zirconia and the stabilizer. It is preferable that the contents of erbium oxide, iron oxide and praseodymium oxide decrease in order from the first layer to the fourth layer.

The pigment content can be theoretically calculated from the amount added to the total mass of zirconia and stabilizer and the manufacturing method.

The calcined body of the present invention preferably has a bending strength of 38 MPa or more, more preferably 40 MPa or more, and even more preferably 42 MPa or more, as measured according to JISR1601.

In the calcined body of the present invention, in the three-point bending test, as shown in the manufacturing method described later, even when the load point is located at the boundary between layers when zirconia powders having different compositions are laminated, the above bending strength can be obtained. For example, if the bending strength is measured by the same test as the bending test of the sintered body described above, a higher strength can be obtained than that of a calcined body produced by simply laminating powders. Also, even if the bending strength is measured by a test in which a load is applied to the boundary, the same strength as that of the calcined body that is not laminated (without boundaries) can be obtained. Also, even if the bending strength is measured by a test in which a load is applied to the boundary, the same strength as that of the calcined body that is not laminated (without boundaries) can be obtained. In the calcined body of the present invention, the bending strength measured by applying a load to the boundary between layers is preferably 90% or more, more preferably 95% or more, of the bending strength of the region other than the boundary (for example, the bending strength of the calcined body produced from a non-laminated composition under the same conditions (for example, the same calcination temperature and calcination time)).

Even if the composition and calcined body of the present invention are subjected to heat treatment for calcination or sintering, peeling does not occur at the boundary between layers in which zirconia powders having different compositions are laminated, and overall deformation can be suppressed. 3 and 4 show schematic diagrams of test pieces for measuring the amount of deformation during sintering. FIG. 3 is a schematic diagram of a two-layer laminate. FIG. 4 is a schematic diagram of a four-layer laminate. FIG. 5 shows a schematic diagram for explaining the method of measuring the deformation amount. For example, a plurality of zirconia powders with different compositions are layered to form a composition, and the composition is fired at 800° C. to 1200° C. for 2 hours to produce a calcined body. Then, as shown in FIGS. 3 and 4, the calcined body is formed into a rectangular parallelepiped shape of width 50 mm×height 10 mm×depth 5 mm by a CAD/CAM system. This becomes the test piece. For example, the two-layer laminate specimen 20 shown in FIG. 3 has a first layer 21a and a second layer 21b. The thickness of the first layer 21a and the thickness of the second layer 21b are each 50% of the total thickness. The four-layer laminate test piece 22 shown in FIG. 4 has a first layer 23a, a second layer 23b, a third layer 23c, and a fourth layer 23d. The thicknesses of the first layer 23a and the fourth layer 23d are each 35% of the total thickness. The thickness of each of the second layer 23b and the third layer 23c is 15% of the total thickness. Assuming that the 50 mm×5 mm surfaces of the test pieces 20 and 22 are the bottom surfaces (upper and lower surfaces), each layer extends in the same direction, preferably parallel to the bottom surfaces 20a and 22a. That is, the boundaries between the layers are parallel to the bottom surfaces 20a and 22a. When this test piece is fired at 1500° C. for 2 hours to be sintered, the bottom surfaces 20a and 22a are deformed so as to be curved. The test pieces 20 and 22 are placed on a flat place (ground plane 30) with the concave side of the bottom surfaces 20a and 22a facing downward. Then, the width of the test pieces 20 and 22 after deformation, that is, the distance L between the contact portions in the width direction is measured. Further, the distance d of the largest portion of the distances between the concavely deformed bottom surfaces 20a and 22a and the ground plane 30 is measured. Then, the deformation amount is calculated as (d/L×100). The amount of deformation is preferably 0.15 or less, more preferably 0.1 or less, more preferably 0.05 or less, and even more preferably 0.03 or less.

A composition and a calcined body produced by laminating zirconia powders with different compositions are easily deformed when sintered, but according to the composition and the calcined body of the present invention, the amount of deformation can be reduced compared to the composition and the calcined body produced by simply laminating. Thereby, the dimensional accuracy of the final product can be improved. For example, the composition and calcined body of the present invention can be suitably applied to dental prostheses that vary greatly among individuals. 3 and 4, for the sake of simplification, a mixed layer of upper and lower layers presumed to be formed at the boundary of each layer is not shown.

The composition of the present invention also includes powders, fluids obtained by adding powders to a solvent, and compacts obtained by molding powders into a predetermined shape. That is, the composition may be in the form of a powder, a paste, or a wet composition (ie, may be in or contain a solvent). The composition may also contain additives such as binders and pigments. Note that the mass of additives such as solvents and binders is not taken into account in the calculation of the above content.

When the composition of the present invention is a molded article, it may be molded by any molding method, such as press molding, injection molding, stereolithography, or may be molded in multiple stages. For example, the composition of the present invention may be press-molded and then subjected to CIP (Cold Isostatic Pressing) treatment.

The calcined body of the present invention can be obtained by firing the composition of the present invention at 800° C. to 1200° C. under normal pressure.

The calcined body of the present invention becomes the zirconia sintered body of the present invention by firing at 1350° C. to 1600° C. under normal pressure.

The length (thickness) of the composition and the calcined body in the stacking direction is preferably determined in consideration of sintering shrinkage so that the sintered body has a target length. For example, when a sintered body produced from the composition and the calcined body is used as a dental material, for example, the target length of the sintered body in the stacking direction is 5 mm to 18 mm, and the length (thickness) of the composition and the calcined body in the stacking direction can be set to 10 mm to 26 mm.

Next, an example of the method for producing the composition, calcined body and sintered body of the present invention will be described. Here, a method for gradually changing the color of the sintered body (gradation) will also be described.

First, the zirconia and stabilizer are wet mixed in water to form a slurry. The slurry is then dried and granulated. Next, the granules are calcined to produce a primary powder.

Next, when applying gradation to the sintered body, the primary powder is divided into two. Next, a pigment is added to at least one of the two primary powders so that the pigment addition rate is different. For example, one may be unpigmented and the other may be pigmented. Hereinafter, the powder with the lower addition rate of the specific pigment is referred to as the low addition rate powder, and the secondary powder with the higher addition rate of the specific pigment is referred to as the high addition rate powder. The amount of pigment added in the high addition rate powder is preferably matched to the amount added in the darkest region of the sintered body. Then, for each, zirconia is pulverized and mixed in water to a desired particle size to form a zirconia slurry. Next, the slurry is dried and granulated to produce a secondary powder. When adding additives such as aluminum oxide, titanium oxide, and binders, they may be added during the production of the primary powder, or may be added during the production of the secondary powder.

Next, based on the secondary powders of the low addition rate powder and the high addition rate powder, a plurality of powders having different pigment content ratios are produced. For example, when the composition and the calcined body of a total of four layers described above are produced, the first powder for the first layer is 100% of the high-addition-rate powder without mixing the low-addition-rate powder. The second powder for the second layer is mixed at a ratio of low addition rate powder:high addition rate powder=5:95 to 15:85. The third powder for the third layer is mixed at a ratio of low addition rate powder:high addition rate powder=35:65 to 45:55. The fourth powder for the fourth layer is mixed at a ratio of low addition rate powder:high addition rate powder=45:55 to 55:45. As another mixing ratio, for example, when the composition and the calcined body of a total of four layers described above are produced, the first powder for the first layer is 100% of the high-addition-rate powder without mixing the low-addition-rate powder. The second powder for the second layer is mixed at a ratio of low addition rate powder:high addition rate powder=10:90 to 30:70. The third powder for the third layer is mixed at a ratio of low addition rate powder:high addition rate powder=70:30 to 90:10. The fourth powder for the fourth layer is 100% low-addition-rate powder without mixing high-addition-rate powder.

When the zirconia sintered body is used as a dental material, it is preferable to make the compounding difference between the second layer and the third layer larger than the compounding difference between the first layer and the second layer and the compounding difference between the third layer and the fourth layer. This makes it possible to reproduce color change similar to that of natural teeth.

In this way, by adjusting the pigment content of each layer based on two types of powders that make the sintered body exhibit different colors, the colors can be naturally changed by laminating each powder in order (gradation can be created).

When laminating for purposes other than coloring, the secondary powder is divided into the number of layers to be laminated. Desired additives may be added to each powder.

Next, a plurality of powders having different pigment contents are stacked in order. When forming a gradation on the sintered body, it is preferable to laminate so that the addition rate of a specific pigment increases or decreases stepwise in the order of lamination. First, after the mold is filled with the powder for the first layer, the upper surface of the powder for the first layer is flattened. As a method of flattening, for example, a method of vibrating the mold or a method of scraping off the upper surface of the first layer of powder can be adopted. However, it is preferable not to apply the press treatment until all the layers are laminated. Next, the powder of the second layer is filled on the powder of the first layer. Next, vibrate the mold. Allow vibrations to be transmitted to the powder in the mold. As a method for imparting vibration, for example, a desired method such as imparting mechanical vibration to the mold, manually shaking the mold, or hitting the mold with a hammer or the like can be employed. As a result, it is considered that the powders of the first layer and the powders of the second layer are partially mixed at the boundary between the powder of the first layer and the powder of the second layer. That is, the number and intensity of vibrations, and in the case of mechanical vibration, the frequency, amplitude, etc. can be appropriately set according to the particle size, particle size distribution, particle shape, etc. of the powder so that the powders of the upper and lower layers are mixed at the boundary between the layers. Next, the upper surface of the powder for the second layer is smoothed in the same manner as the powder for the first layer. This operation is repeated until all layers are laminated.

For example, when producing the four-layer composition and the calcined body described above, the mold is filled with the first powder to a predetermined thickness (eg, 25% to 45% of the total thickness). At this time, the upper surface of the first powder is flattened, but is not pressed. Next, the first powder is filled with the second powder to a predetermined thickness (for example, 5% to 25% of the total thickness). Next, vibrate the mold. It is presumed that this vibration forms a first boundary layer in which the first powder and the second powder are mixed at the boundary between the upper surface of the first powder and the lower surface of the second powder. Next, the upper surface of the second powder is flattened. The second powder is not pressed before filling the third powder. Next, the third powder is filled up to a predetermined thickness (for example, 5% to 25% of the total thickness) on the second powder. Next, vibrate the mold. It is presumed that this vibration forms a second boundary layer in which the second powder and the third powder are mixed at the boundary between the upper surface of the second powder and the lower surface of the third powder. Next, the upper surface of the third powder is flattened. The third powder is not pressed before filling the fourth powder. Next, the fourth powder is filled up to a predetermined thickness (for example, 25% to 45% of the total thickness) on the third powder. Next, vibrate the mold. It is presumed that this vibration forms a third boundary layer in which the third powder and the fourth powder are mixed at the boundary between the upper surface of the third powder and the lower surface of the fourth powder.

After laminating all the layers, press molding is performed to produce a molding as the composition of the present invention. The molding may be further subjected to CIP treatment.

By not performing a pressing process before filling the powder of the next layer and by applying vibration each time each layer is filled, a boundary layer in which the powders of the upper and lower layers are mixed can be formed between adjacent layers. Thereby, in the sintered body, the adhesion between adjacent layers can be enhanced. The shrinkage amount or shrinkage rate during heat treatment can be made equal for each layer, and separation between layers during heat treatment or distorted deformation of the sintered body against the target shape can be prevented. Additionally, color differences between adjacent layers can be mitigated. Thereby, in the sintered body, the color can be naturally changed in the stacking direction (gradation can be created).

Also, this method does not require an intermediate layer between each primary layer. That is, when laminating four main layers, only four layers need to be laminated. In addition, press processing is not required for each layer. As a result, labor and time can be greatly reduced, and manufacturing costs can be reduced.

When a calcined body is not produced, the composition is fired at 1400° C. to 1600° C., preferably 1450° C. to 1550° C. to sinter the zirconia powder to produce the zirconia sintered body of the present invention. It may be molded into a desired shape at the molding stage.

When producing a calcined body, the composition is sintered at 800° C. to 1200° C. to produce a calcined body. Next, the calcined body is fired at 1400° C. to 1600° C., preferably 1450° C. to 1550° C. to sinter the zirconia powder and produce the zirconia sintered body of the present invention. Forming may be performed by cutting or the like at the stage of the calcined body, or may be performed after sintering. Molding can be performed in a CAD/CAM system.

The method for producing a dental prosthesis is the same as the above method for producing a sintered body, except that the calcined body or sintered body is formed into a crown shape.

In the above embodiment, the composition, the calcined body, and the sintered body based on the four-layer laminate were exemplified, but the number of layers is not limited to four. For example, it may be a composition, a calcined body, or a sintered body produced from a two-layer laminate of the first layer and the fourth layer described above. Alternatively, it may be a composition, a calcined body and a sintered body made from the above-described first, second and fourth layers or a three-layer laminate of the first, third and fourth layers. FIG. 2 is for facilitating explanation of the positional relationship and direction of each point, and the shape and dimensions are not limited to those shown in FIG.

[Examples 1 to 4]
[Production of composition, calcined body and sintered body]
A sintered body was produced based on a composition produced by laminating zirconia powders having different compositions, and bending strength, chromaticity, and deformation were measured.

First, zirconia powder containing a stabilizer was produced. To 92.8% by weight of predominantly monoclinic zirconia powder, 7.2% by weight (4 mol%) of yttria was added as a stabilizer. Alumina sol was added to the mixed powder (100% by mass) of zirconia and yttria so as to add 0.1% by mass of alumina, and 150% by mass of water, 0.2% by mass of an antifoaming agent, and 1% by mass of a dispersant were added to the mixed powder of zirconia and yttria (100% by mass), and the mixture was pulverized in a ball mill for 10 hours. The average particle size of the slurry produced after pulverization was 0.12 μm. Next, the mixture was granulated with a spray dryer, and the granules thus obtained were calcined at 1000° C. for 2 hours to prepare a primary powder.

Next, the primary powder was divided into two and pigment was added to at least one of them. Powders with a low pigment addition rate were designated as low addition rate powders, and those with a high pigment addition rate were designated as high addition rate powders. Table 1 shows the addition rates of Examples 1-3. Table 4 shows the addition rate of Example 4. The numerical values shown in Tables 1 and 2 are addition rates to mixed powder (100% by mass) of zirconia and yttria. In addition, to each powder, 0.2% by mass of titania, 200% by mass of water, 0.2% by mass of an antifoaming agent, and 1% by mass of a dispersant were added to the mixed powder (100% by mass) of zirconia and yttria, and the mixture was pulverized in a ball mill for 15 hours. The average particle size of the slurry produced after pulverization was 0.13 μm. Next, 6% by mass of binder and 0.5% by mass of release agent were added and mixed for 15 minutes in a ball mill. Next, the resulting slurry was granulated with a spray dryer to prepare secondary powders of a low addition rate powder and a high addition rate powder.

Next, the low addition rate powder and the high addition rate powder were mixed at the ratios shown in Tables 3 to 6 to prepare first to fourth powders.

Next, a molded body was produced. In Examples 1, 3 and 4, 35 g of the first powder was filled in a mold having an inner dimension of 82 mm×25 mm, and the top surface of the first powder was leveled by scraping the top surface. Next, 15 g of the second powder was filled on the first powder, and the mold was vibrated by a vibration device. After that, the upper surface of the second powder was leveled by scraping the upper surface of the second powder. Next, 15 g of the third powder was filled on the second powder, and the mold was vibrated by a vibration device. After that, the upper surface of the third powder was leveled by scraping the upper surface of the third powder. Next, 35 g of the fourth powder was filled on the third powder, and the mold was vibrated by a vibration device. After that, the upper surface of the fourth powder was leveled by scraping the upper surface of the fourth powder. Example 2 was the same as Examples 1, 3 and 4 except that 50 g of the first powder and 50 g of the second powder were filled. Next, the upper mold was set, and primary press molding was performed for 90 seconds with a uniaxial press molding machine at a surface pressure of 200 kg/cm ² . Next, the primary press molded body was subjected to CIP molding at 1500 kg/cm ² for 5 minutes to produce a molded body.

Next, the compact was fired at 1000° C. for 2 hours to prepare a calcined body. Next, a CAD/CAM system (Katana System, Kuraray Noritake Dental Co., Ltd.) was used to form a crown shape. Next, the calcined body was fired at 1500° C. for 2 hours to produce a sintered body. The length of the sintered body in the stacking direction of the first to fourth powders was 18 mm.

In any of the sintered bodies of Examples 1 to 4, a gradation that changes from light yellow to yellowish white is formed from the region corresponding to the first layer of the composition toward the region corresponding to the fourth layer, and the appearance is similar to that of natural teeth.

[Measurement of bending strength]
The bending strength of the calcined body and sintered body produced in Example 4 was measured according to JISR1601. As a comparative example, bending strength was also measured for a calcined body and a sintered body which were not vibrated when each powder was filled. Comparative Example 1 is a calcined body and a sintered body produced from a composition that is not press-treated each time each layer is filled. Comparative Example 2 is a calcined body and a sintered body produced from a composition subjected to press treatment every time each layer is filled. Bending strength was measured according to JISR1601. However, the test piece was cut out along the stacking direction in the longitudinal direction. A portion of the test piece corresponding to the boundary between the powders (mixed layer) extends along the load application direction (along the direction of the smallest area) and traverses the test piece. Table 7 shows the results of measuring the bending strength by setting the load point of the three-point bending test to the position of the portion corresponding to the mixed layer between the second powder and the third powder in the test piece.

Regarding the calcined bodies, the bending strength of Example 4 was 40 MPa or more, but the bending strength of Comparative Examples was 36 MPa or less. From this, it can be seen that the bonding strength between the layers can be increased at the stage of the calcined body by applying vibration during powder lamination. As for the sintered body, in Example 4, it was 1200 MPa or more, but in Comparative Examples 1 and 2, it was less than 1100 MPa and 100 MPa or more, which was lower than that in Example 4. As for the sintered body, it can be seen that the bonding strength between the layers can be increased similarly.

In addition, as shown in Example 9 below, the bending strength of Example 4 is the same as the bending strength of the sintered body produced without lamination in both the sintered body and the calcined body. From this, it can be seen that by applying vibration during powder lamination, the boundary between layers has the same strength as the region other than the boundary in both the sintered body and the calcined body.

Primarily, this is presumed to be due to the fact that the powders of the upper and lower layers were partially mixed at the boundaries by applying vibrations during powder lamination of each layer, thereby increasing the bonding strength between the layers. Secondly, since the first to fourth powders were produced by mixing two kinds of powders, it is presumed that the difference in properties between the powders was small, and that they were easy to mix.

[Measurement of fracture toughness]
The fracture toughness of the sintered body produced in Example 4 was measured according to JISR1607. The locations of the boundaries in the specimen are the same as for the bend test described above. Also, the presser is aligned with the position of the boundary between the second powder and the third powder. As a result, the fracture toughness was also 4.3 MPa·m ^1/2 . As shown in Example 9 below, this numerical value is similar to the fracture toughness of a sintered body produced without lamination, indicating that lamination does not cause a decrease in fracture toughness.

[Measurement of shrinkage deformation amount during sintering]
In Example 4, the calcined body produced by calcining at 1000 ° C. for 2 hours was used to prepare the test pieces shown in FIGS. 3 and 4, and the test pieces were sintered at 1500 ° C. for 2 hours. The deformation amount was measured by the same method as described above. Also, as a comparative example, the same test piece was produced for Comparative Example 1 and Comparative Example 2 in the same manner as in the bending test, and the amount of deformation after sintering was measured. Table 8 shows the measurement results.

In the comparative examples, the deformation amount was 0.15 or more. On the other hand, in Example 4, the amount of deformation can be reduced to 0.05 or less, and it can be seen that the amount of deformation can be greatly suppressed as compared with the comparative example. From this, it is considered that shrinkage deformation during sintering can be suppressed by applying vibration to the composition when laminating powders having different compositions.

Moreover, comparing Comparative Example 1 and Comparative Example 2, Comparative Example 1 has a smaller amount of deformation. From this, it is considered that shrinkage deformation during sintering can be further suppressed by not applying a press treatment after filling each layer.

Furthermore, comparing the two-layer laminate and the four-layer laminate, the deformation amount is smaller in the four-layer laminate than in the two-layer laminate. From this, it is considered that shrinkage deformation can be further suppressed by increasing the number of layers.

[Measurement of chromaticity and color difference]
For each of the first powder, second powder, third powder, and fourth powder in Examples 1 to 4, individual sintered bodies were produced, and the chromaticity was measured according to the L ^* a ^* b ^* color system. The chromaticity was measured by processing the sintered body into a disk having a diameter of 14 mm and a thickness of 1.2 mm, polishing both surfaces of the disk, and then measuring the chromaticity using a measuring device CE100-DC/US manufactured by Olympus. Further, color differences ΔE ^* ab _{1 to 3} between adjacent layers were calculated based on the chromaticity measurement results. Further, the color difference ΔE ^* _ab4 between the first layer and the fourth layer was calculated. Then, (ΔE ^* ab ₁ +ΔE ^* ab ₂ +ΔE ^* ab ₃ )−ΔE ^* ab ₄ was calculated. Chromaticity is shown in Tables 9-12. Table 13 shows the color difference.

It is considered that the chromaticity of the sintered body of each powder represents the chromaticity of the color partially exhibited by the zirconia sintered body.

In the sintered body of the first layer of the four-layer laminate, L ^* was 58-73, a ^* was 0-8, and b ^* was 14-27. In the sintered body of the second layer, L ^* was 64-73, a ^* was 0-6, and b ^* was 16-22. In the sintered body of the third layer, L ^* was 70 to 78, a ^* was −2 to 2, and b ^* was 5 to 17. In the sintered body of the fourth layer, L ^* was 72 to 84, a ^* was −2 to 1, and b ^* was 4 to 15.

The color difference between the sintered body of the first layer and the sintered body of the second layer was 7-14. The color difference between the second layer sintered body and the third layer sintered body was 10-18. The color difference between the third layer sintered body and the fourth layer sintered body was 4-9. The color difference between the first layer sintered body and the fourth layer sintered body was 28-36. The value obtained by subtracting the color difference between the first layer sintered body and the fourth layer sintered body from the sum of the color difference between the first layer sintered body and the second layer sintered body, the color difference between the second layer sintered body and the third layer sintered body, and the color difference between the third layer sintered body and the fourth layer sintered body was 1 or less.

[Example 5]
[measurement of change in b ^* value]
A low-addition-rate powder and a high-addition-rate powder were prepared by adding a pigment at the addition rate shown in Table 14 to a mixed powder of zirconia and yttria (100% by mass), and a composition was produced at the mixing rate shown in Table 15. A sintered body was produced in the same manner as in Examples 1 to 4, and the change in the b ^* value of the L ^* a ^* b ^* color system along the stacking direction (along the second direction Y in FIG. 1) was measured. FIG. 6 shows a schematic diagram of the prepared test piece and the measurement results. The upper diagram in FIG. 6 is a schematic diagram of the test piece, showing dimensions and measurement directions. The lower diagram in FIG. 6 is a graph showing the measurement results. A sintered specimen was made to have dimensions of 20 mm×20 mm×1 mm after sintering. The first layer is the area filled with the first powder, and the fourth layer is the area filled with the fourth powder. The b ^* value was measured using a two-dimensional colorimeter RC-300 manufactured by Paparabo Co., Ltd., placing a test piece in the center of a 29 mm × 22 mm size image, scanning in the direction perpendicular to the boundary surface of each layer, and measuring at intervals of about 13 μm. The numerical values on the X-axis of the lower graph in FIG. 6 indicate the number of measurement points. As Comparative Example 3, changes in the b ^* value were similarly measured for a sintered body produced by applying no vibration when laminating the powder of each layer and performing press processing every time each layer was filled. The composition and mixing ratio of the low-addition-rate powder and the high-addition-rate powder in Comparative Example 3 are the same as in Example 5. FIG. 7 shows a schematic diagram of the test piece and the measurement results.

Looking at the graph in FIG. 7, it can be seen that the b ^* value tends to flatten out in the central portion of each layer. Moreover, at the boundary between the layers, a step-like sharp change in the b ^* value is also observed. It is considered that this is because the powders of each layer with different pigment compositions are sintered independently. According to this, the appearance of the test piece of Comparative Example 3 does not form a clear gradation. On the other hand, looking at the graph in FIG. 6, the b ^* values tend to increase gently even in the central portion of each layer. Moreover, no step-like change in b ^* value is observed at the boundary between layers, and it is difficult to determine where the boundary is. In particular, the transition is linear at the boundary between the first and second layers and the boundary between the third and fourth layers. According to this, it can be seen that the appearance of the sintered body of the present invention has a fine gradation. This result is considered to be due to the fact that, in the present invention, the powders were mixed between the adjacent layers near the boundary between the upper and lower layers due to the vibration applied when the first to fourth powders were filled, and the difference in the pigment content between the adjacent layers became small. Since the difference in pigment content between the second powder and the third powder is large, it is thought that the change in the b ^* value in the graph also changes more rapidly than in the other portions.

[Examples 6 to 15]
A sintered body to be a dental prosthesis was produced based on a composition produced by laminating zirconia powders having different pigment compositions. Also, the chromaticity of the sintered body of each powder on which each layer is based was measured. Furthermore, the sintered body according to Example 9 was measured for bending strength, fracture toughness, and monoclinic peak ratio after hydrothermal treatment.

First, primary powder was produced in the same manner as in Examples 1-4. The primary powder was then divided into four. These powders are referred to as first to fourth powders. In Examples 6-15, pigments shown in Tables 6-16 below were added to each powder. The numerical values shown in the table are the addition rates to the mixed powder (100% by mass) of zirconia and yttria. Secondary powders of the first to fourth powders were prepared in the same manner as in Examples 1 to 4, except that the low addition rate powder and the high addition rate powder were not prepared and the addition rate of the pigment.

Next, molded bodies were produced in the same manner as in Examples 1-4. Next, the compact was fired at 1000° C. for 2 hours to prepare a calcined body. Next, a CAD/CAM system (Katana System, Kuraray Noritake Dental Co., Ltd.) was used to form a crown shape. Next, the calcined body was fired at 1500° C. for 2 hours to produce a sintered body. The length of the sintered body in the stacking direction of the first to fourth powders was 8 mm.

In any of the sintered bodies of Examples 6 to 16, a gradation that changes from light yellow to yellowish white is formed from the region corresponding to the first layer of the composition toward the region corresponding to the fourth layer, and the appearance is similar to that of natural teeth.

In the same manner as in Examples 1 to 4, the chromaticity and color difference of the sintered bodies of the first, second, third and fourth powders were measured. Chromaticity is shown in Tables 26-35. Color differences are shown in Tables 36-37.

It is considered that the chromaticity of each powder represents the chromaticity of each point of a zirconia sintered body produced from a laminate of a plurality of powders. The combination of the four sintered bodies of Example 9 exhibited a bright color as a whole. The combination of the four sintered bodies of Example 10 exhibited a dark color as a whole.

In the sintered body of the first layer, L ^* was 58 to 76, a ^* was −2 to 8, and b ^* was 5 to 27. In the sintered body of the second layer, L ^* was 66 to 81, a ^* was −2 to 6, and b ^* was 4 to 21. In the sintered body of the third layer, L ^* was 69 to 83, a ^* was −2 to 2, and b ^* was 3 to 17. In the sintered body of the fourth layer, L ^* was 71 to 84, a ^* was −2 to 1, and b ^* was 2 to 15.

The color difference between the sintered body of the first layer and the sintered body of the second layer was 3-15. The color difference between the second layer sintered body and the third layer sintered body was 1-11. The color difference between the third layer sintered body and the fourth layer sintered body was 1-4. The color difference between adjacent layers tended to decrease from the first layer to the fourth layer. The color difference between the sintered body of the first layer and the sintered body of the fourth layer was 8-29. The value obtained by subtracting the color difference between the first layer sintered body and the fourth layer sintered body from the sum of the color difference between the first layer sintered body and the second layer sintered body, the color difference between the second layer sintered body and the third layer sintered body, and the color difference between the third layer sintered body and the fourth layer sintered body was 1 or less.

For the first powder, second powder, third powder, and fourth powder in Example 9, individual zirconia sintered bodies were produced, and bending strength, fracture toughness, and monoclinic peak ratio after hydrothermal treatment were measured. Table 38 shows the measurement results. The bending strength of the zirconia sintered body was measured according to JISR1601. The fracture toughness of the zirconia sintered body was measured according to JISR1607. The hydrothermal treatment test complied with ISO13356 under conditions of 180°C, 1 MPa, and 5 hours. After the hydrothermal treatment test, the X-ray diffraction pattern of the zirconia sintered body was measured with CuKα rays to measure the monoclinic peak ratio, that is, the degree of phase transition to monoclinic crystal due to the hydrothermal treatment test. All sintered bodies had a bending strength of 1200 MPa or more, a fracture toughness of 4 MPa·m ^1/2 or more, and a monoclinic peak ratio of 1 or less. Since the zirconia sintered bodies in other examples have the same composition, it is considered that similar results can be obtained. Flexural strength and fracture toughness test results were similar to those when the laminate boundary was loaded.

In addition, for the second powder, the bending strength of a calcined body produced by sintering at 1000° C. for 2 hours was also measured according to JISR1601. The bending strength of the calcined body of the second powder was 41 MPa. This number was similar to the number when the laminate boundary was loaded and tested.

[Example 16]
In the above examples, the content of yttria was 4 mol % in terms of the total number of moles of zirconia and yttria. The sintered body used for the measurement is the same as that of Example 4 shown in Tables 14 and 15, except for the content of yttria. Table 39 shows the measurement results. When compared with the chromaticities shown in Table 12, when the yttria content was lowered, L ^* tended to decrease and a ^* and b ^* tended to increase.

The zirconia sintered body of the present invention and the composition and calcined body for the zirconia sintered body have been described based on the above embodiments, but are not limited to the above embodiments, and within the scope of the present invention and based on the basic technical idea of the present invention. Also, within the scope of the claims of the present invention, various combinations, replacements, or selections of various disclosure elements (including each element of each claim, each element of each embodiment or example, each element of each drawing, etc.) are possible.

Further tasks, objects and developments of the invention are also made clear from the entire disclosure of the invention including the claims.

Any numerical range recited herein should be construed to specifically recite any numerical value or subrange within the range, even if not otherwise specified.

Some or all of the above embodiments may be described in the following supplementary remarks, but are not limited to the following description.
[Appendix 1]
Forming a plurality of zirconia powders with different compositions containing zirconia and a stabilizer that suppresses the phase transition of zirconia,
laminating the plurality of zirconia powders to form a zirconia composition;
A calcined zirconia body produced by firing the zirconia composition at 800° C. to 1200° C.,
A test piece is obtained by molding the calcined body into a rectangular parallelepiped shape with dimensions of 50 mm in width × 10 mm in height × 5 mm in depth.
calcining the test piece at 1500 ° C. for 2 hours,
Of the two bottom surfaces, when placed with the bottom surface deformed into a concave surface facing down,
A zirconia calcined body, wherein (maximum distance between the bottom surface deformed into a concave surface and the contact surface)/(distance between the contact portions in the width direction)×100 is 0.15 or less.
[Appendix 2]
The zirconia calcined body according to the appendix, wherein (maximum distance between the bottom surface deformed into a concave surface and the contact surface)/(distance between the contact portions in the width direction)×100 is 0.1 or less.
[Appendix 3]
The zirconia calcined body according to the supplementary note, wherein the plurality of zirconia powders contain a pigment, and the content of the pigment is different from each other.
[Appendix 4]
A zirconia sintered body characterized by being produced by a method including a step of sintering a zirconia calcined body according to the appendix at 1400°C to 1600°C.
[Appendix 5]
A step of producing a plurality of lamination powders containing zirconia, a stabilizer that suppresses the phase transition of zirconia, and a pigment, and having different content rates of the pigment;
A stacking step of stacking a plurality of the stacking powders in a mold,
A method for producing a zirconia composition, wherein in the lamination step, the mold is vibrated after at least two of the lamination powders are filled in the mold.
[Appendix 6]
The method for producing a zirconia composition according to the appendix, wherein in the lamination step, the mold is vibrated each time one of the lamination powders is filled into the mold.
[Appendix 7]
A step of producing a low-addition-rate powder and a high-addition-rate powder containing zirconia, a stabilizer that suppresses the phase transition of zirconia, and a pigment, and having different pigment contents;
a mixing step of mixing the low addition rate powder and the high addition rate powder to prepare at least one lamination powder;
A stacking step of stacking at least two powders of the low addition rate powder, the high addition rate powder and the stacking powder in a mold;
A method for producing a zirconia composition, comprising:
[Appendix 8]
The method for producing a zirconia composition according to the appendix, wherein in the layering step, the mold is vibrated after filling the mold with at least two powders.
[Appendix 9]
In the mixing step, two or more of the lamination powders having different mixing ratios of the low-addition-rate powder and the high-addition-rate powder are prepared,
The method for producing a zirconia composition according to the appendix, wherein in the layering step, a plurality of powders are layered such that the content of the low-addition-rate powder or the high-addition-rate powder changes in order.
[Appendix 10]
The method for producing a zirconia composition according to the appendix, wherein in the layering step, after filling one powder into the mold, the upper surface of the powder is flattened.
[Appendix 11]
The method for producing a zirconia composition according to the appendix, wherein in the layering step, the powder is layered such that the content of the pigment in the powder changes in order.
[Appendix 12]
A method for producing a zirconia composition according to the appendix;
calcining the composition at 800° C. to 1200° C.;
A method for producing a zirconia calcined body, comprising:
[Appendix 13]
A method for producing a zirconia composition according to the appendix;
calcining the composition at 1400° C. to 1600° C.;
A method for producing a zirconia sintered body, comprising:
[Appendix 14]
A method for manufacturing a zirconia calcined body described in the appendix;
a step of firing the calcined body at 1400° C. to 1600° C.;
A method for producing a zirconia sintered body, comprising:

The zirconia sintered body of the present invention can be used in various applications such as dental materials such as prosthetics, optical fiber connection parts such as ferrules and sleeves, various tools (e.g., grinding balls, grinding tools), various parts (e.g., screws, bolts and nuts), various sensors, electronic parts, and ornaments (e.g., watch bands). When zirconia sintered bodies are used as dental materials, for example, copings, frameworks, crowns, crown bridges, abutments, implants, implant screws, implant fixtures, implant bridges, implant bars, brackets, denture bases, inlays, onlays, onlays, orthodontic wires, laminated veneers, etc.

10 zirconia sintered body 20, 22 calcined body 20a, 22a bottom surface 21a, 21b first layer, second layer 23a to 23d first to fourth layer 30 ground surface A to D first to fourth point P one end Q other end X first direction Y second direction

Claims (25)

A zirconia sintered body in which a plurality of zirconia powders containing zirconia and yttria as a stabilizer that suppresses the phase transition of zirconia and having different compositions due to different pigment contents are laminated and vibrated to form a mixed layer in which the upper and lower zirconia powders are partially mixed at each boundary between the zirconia powders, and the laminated body obtained by molding is sintered,
A test piece cut out from the zirconia sintered body in the longitudinal direction along the stacking direction,
According to JISR 1601, the test piece in which the mixed layer crosses the test piece along the direction of load application, and the bending strength measured by aligning the load point of the three-point bending test with the position of the mixed layer is 1100 MPa or more.
A zirconia sintered body characterized by: 2. The zirconia sintered body according to claim 1, wherein said bending strength is 1200 MPa or more. Another test piece cut in the longitudinal direction along the lamination direction from the zirconia calcined body in which the laminated body was calcined at 800 ° C. to 1200 ° C.
According to JISR 1601, the bending strength measured by aligning the load point of the three-point bending test with the position of the mixed layer for the other test piece in which the mixed layer crosses the other test piece along the load application direction Satisfies the test condition that one of the zirconia powders alone is 90% or more of the bending strength of another test piece calcined at the same temperature as the calcining temperature of the other test piece.
The zirconia sintered body according to claim 1 or 2, characterized by: The zirconia sintered body according to any one of claims 1 to 3, wherein the plurality of zirconia powders contain pigments and have different pigment contents. The zirconia sintered body according to any one of claims 1 to 4, wherein each sintered body obtained by sintering the plurality of zirconia powders alone at 1500 ° C. has a bending strength of 1100 MPa or more measured in accordance with JISR1601. A zirconia calcined body is prepared by calcining the laminate at 800 ° C. to 1200 ° C.,
A test piece is obtained by molding the zirconia calcined body into a rectangular parallelepiped shape with dimensions of 50 mm in width × 10 mm in height × 5 mm in depth.
calcining the test piece at 1500 ° C. for 2 hours,
Of the two bottom surfaces, when placed with the bottom surface deformed into a concave surface facing down,
The zirconia sintered body according to any one of claims 1 to 5, wherein (maximum distance between the bottom surface deformed into a concave surface and the ground contact surface) / (distance between the contact portions in the width direction) x 100 is 0.15 or less. On a straight line extending in the first direction from one end to the other end,
Chromaticity (L ^{*, a*, b*) by the L* a *} b ^* color system of the first point in the section from the one end to 25% of the total length is defined as (L1, ^a1 , ^b1 ),
When the chromaticity (L ^* , a ^* , b ^* ) according to the L ^* a ^* b ^* color system of the second point in the section from the other end to 25% of the total length is (L2, a2, b2),
On a straight line connecting the first point and the second point,
There is no section where the L ^* value decreases by 1 or more from the first point to the second point,
There is no section where the a ^* value increases by 1 or more from the first point to the second point,
The zirconia sintered body according to any one of claims 1 to 6, wherein there is no section where the b ^* value increases by 1 or more from the first point to the second point. Let the chromaticity (L ^* , a ^* , b ^* ) by the L ^* a ^* b ^* color system of a third point between the first point and the second point on the straight line connecting the first point and the second point be (L3, a3, b3),
When the chromaticity (L ^* , a ^* , b ^* ) in the L ^* a ^* b ^* color system at the fourth point between the third point and the second point is (L4, a4, b4),
At the first point, the third point, the fourth point and the second point,
Let ΔL ^* be the difference between the L ^* values at two adjacent points,
The difference between the a ^* values at two adjacent points is Δa ^* ,
Let Δb ^* be the difference between the b ^* values at two adjacent points,
When ΔE ^* ab is calculated from the following formula 1,
ΔE ^* ab between the first point and the third point is 3.7 or more and 14.3 or less,
ΔE ^* ab between the third point and the fourth point is 1.8 or more and 10.5 or less,
ΔE ^* ab between the fourth point and the second point is 1.0 or more and 9.0 or less,
The zirconia sintered body according to claim 7, characterized by:
[Formula 1]

the color changes in a first direction from one end to the other end,
7. The zirconia sintered body according to claim 6, wherein on a straight line from said one end to said other end, there is no change in the increase or decrease tendency of chromaticity according to the L ^* a ^* b ^* color system. The zirconia sintered body according to claim 9, wherein the L ^* value tends to increase, and the a ^* value and b ^* value tend to decrease, from the first point in the section from the one end to 25% of the total length on the straight line connecting the one end and the other end toward the second point in the section from the other end to 25% of the total length. The zirconia sintered body according to any one of claims 7 to 10, wherein the distance from said one end to said other end is 5 mm to 18 mm. The zirconia sintered body according to any one of claims 7 to 11, characterized in that the color does not change along the second direction perpendicular to the first direction. At two points on a straight line extending in the second direction,
Let the difference in L ^* value between the two points be ΔL ^* ,
Let the difference in a ^* value between the two points be Δa ^* ,
Let Δb ^* be the difference in b ^* value between the two points,
When ΔE ^* ab is calculated from Equation 2 below,
13. The zirconia sintered body according to claim 12, wherein ΔE ^* ab is less than 1.
[Formula 2]

The zirconia sintered body according to any one of claims 7 to 13, characterized in that the fracture toughness measured according to JISR1607 is 3.5 MPa·m ^1/2 or more. The zirconia sintered body according to any one of claims 7 to 14, wherein, in the X-ray diffraction pattern of the zirconia sintered body after being subjected to a hydrothermal treatment test at 180 ° C. and 1 MPa for 5 hours, the ratio of the height of the peak present near the position where the [111] peak derived from the tetragonal crystal near 30 ° 2θ occurs is 1 or less. . A zirconia calcined body for producing a zirconia sintered body, characterized in that the zirconia sintered body according to any one of claims 1 to 15 is obtained by sintering at 1400°C to 1600°C. A zirconia calcined body obtained by laminating a plurality of zirconia powders having different compositions by laminating zirconia and yttria as a stabilizer that suppresses the phase transition of zirconia and having different compositions due to different pigment contents, forming a mixed layer in which upper and lower zirconia powders are partially mixed at each boundary between zirconia powders, and calcining the laminated body at 800 ° C. to 1200 ° C.,
A test piece cut out from the zirconia calcined body in the longitudinal direction along the stacking direction,
According to JISR 1601, the test piece in which the mixed layer crosses the test piece along the direction of load application has a bending strength measured by aligning the load point of the three-point bending test with the position of the mixed layer. Satisfies the test condition that the bending strength is 90% or more of the bending strength of another test piece that is calcined at the same temperature as the calcining temperature of the test piece.
A zirconia calcined body characterized by: 18. The zirconia calcined body according to claim 17, wherein the plurality of zirconia powders contain pigments and have different pigment contents. Another test piece is obtained by molding the zirconia calcined body into a rectangular parallelepiped shape with dimensions of 50 mm in width × 10 mm in height × 5 mm in depth.
calcining the other test piece at 1500 ° C. for 2 hours,
Of the two bottom surfaces, when placed with the bottom surface deformed into a concave surface facing down,
19. The zirconia calcined body according to claim 17 or 18, wherein (maximum distance between the bottom surface deformed into a concave surface and the contact surface)/(distance between the contact portions in the width direction) x 100 is 0.15 or less. A zirconia sintered body obtained by firing the zirconia calcined body according to any one of claims 17 to 19. A laminate for producing a zirconia sintered body, characterized in that the zirconia sintered body according to any one of claims 1 to 15 is obtained by sintering at 1400°C to 1600°C. A laminate for producing a zirconia sintered body, characterized in that the zirconia calcined body according to any one of claims 16 to 19 is obtained by firing at 800°C to 1200°C. A dental prosthesis, wherein the zirconia calcined body according to any one of claims 16 to 19 is cut and then sintered. A zirconia sintered body obtained by laminating a plurality of zirconia powders having different compositions by laminating zirconia and yttria as a stabilizer that suppresses the phase transition of zirconia, and applying vibration to form a mixed layer in which the upper and lower zirconia powders are partially mixed at each boundary between the zirconia powders, and sintering the laminated body at 1400 ° C. to 1600 ° C.,
A test piece cut out from the zirconia sintered body in the longitudinal direction along the stacking direction,
According to JISR 1601, the test piece in which the mixed layer crosses the test piece along the load application direction is measured with the load point of the three-point bending test aligned with the position of the mixed layer. Satisfies the test condition that the bending strength is 90% or more of the bending strength of another test piece obtained by sintering one of the zirconia powders alone at the same temperature as the sintering temperature of the test piece.
A zirconia sintered body characterized by: A zirconia calcined body obtained by laminating a plurality of zirconia powders having different compositions by laminating zirconia and yttria as a stabilizer that suppresses the phase transition of zirconia and having different compositions due to different pigment contents, forming a mixed layer in which upper and lower zirconia powders are partially mixed at each boundary between zirconia powders, and calcining the laminated body at 800 ° C. to 1200 ° C.,
A test piece cut out from the zirconia calcined body in the longitudinal direction along the stacking direction,
According to JISR 1601, the test piece in which the mixed layer crosses the test piece along the direction of load application has a bending strength measured by aligning the load point of the three-point bending test with the position of the mixed layer. Satisfies the test condition that the bending strength is 90% or more of the bending strength of another test piece that is calcined at the same temperature as the calcining temperature of the test piece.
A zirconia calcined body characterized by:

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